1. Field of the Invention
This invention relates to heat exchangers and, more particularly, to heat exchangers utilizing tube-to-header joints.
2. Description of Related Art
Heat exchangers of many types, such as radiators, charge air coolers, oil coolers and the like, suffer limited life as a result of high working stresses at their tube-to-header joints. These stresses are a result of thermal expansion and contraction of the tubes, thermal changes in header length, and variations in internal pressure during operation. Since the tubes are usually rigidly attached to a relatively inflexible header by means of soldering, brazing, welding or the like, the resulting stresses ultimately lead to joint fatigue failure or tube fatigue in the area next to the joint.
In an effort to minimize or eliminate the stresses described above, some heat exchangers have been made with grommeted tube-to-header joints. In such heat exchangers, tube openings in the headers are made to be oversize with respect to the tubes. These openings are fitted with resilient grommets, usually made of high temperature silicone rubber. The grommets have slightly smaller openings than the tubes, so that when the tubes are pushed through the grommets the compression fit provides a leak-free connection of each tube to the header. The heat exchanger assembly involves the tedious handling of numerous small parts (the grommets), and lacks any real bond between the tubes and the headers, relying solely on the compression fit to provide a seal. To achieve the desired compression fit with the grommets, the fit and alignment of the core tubes to the grommeted header openings must be critically maintained through close dimensional tolerances. A major disadvantage of this design is that sealing is dependent on providing and maintaining a compression fit between the grommet, tube, and header.
Heat exchangers have also been made with specially made resilient headers. In such heat exchangers, a rigid metal header with oversized tube openings accepts loosely fitted brass ferrules in each tube opening. The brass ferrules are then bonded to the metal header by molding silicone rubber around each ferrule. The brass ferrules are later soldered to brass heat exchanger tubes.
The disadvantages of specially made resilient headers include the substantial amount of skill and labor required to solder the tubes and headers together. Further, great care must be exercised in the soldering operation to prevent destruction of the silicone bond to the ferrules. Also, the specially molded resilient headers are extremely expensive to produce.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of manufacturing a heat exchanger having long-life properties.
It is another object of the present invention to provide a method of manufacturing a heat exchanger with resilient headers or resilient tube-to-header joints.
It is a further object of the present invention to provide a method of manufacturing a heat exchanger having long-life properties and which is substantially simpler to manufacture.
It is another object of the present invention to provide a method of manufacturing a heat exchanger which requires fewer parts.
It is a further object of the present invention to provide a method of manufacturing a heat exchanger which requires less critical dimensional tolerances.
It is yet another object of the present invention to provide a method of manufacturing a heat exchanger which provides improved joint integrity.
It is still another object of the present invention to provide a method of manufacturing a heat exchanger which is easier to assemble.
It is another object of the present invention to provide a method of manufacturing a heat exchanger which provides a resilient tank to header joint.
It is a further object of the present invention to provide a heat exchanger which includes a resiliently bonded tube-to-header joint.
It is another object of the present invention to provide a heat exchanger which includes a sealing joint using compression and bonding.
It is another object of the present invention to provide a heat exchanger which includes a resilient joint including a bonded grommet.
It is another object of the present invention to provide a heat exchanger which includes a resilient tank to header joint.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.